Multiple signaling events are required for NAADP synthesis by DUOX2 and formation of Ca2+ microdomains to initiate T cell activation.

T cell activation critically depends on the calcium ion (Ca2+)-mobilizing second messenger NAADP (nicotinic acid adenine dinucleotide phosphate), which induces the formation of Ca2+ microdomains that initiate global Ca2+ signals. NAADP is produced in immune synapses in T cells by dual NADPH oxidase 2 (DUOX2). Here, we investigated the mechanisms that stimulate DUOX2 activity in T cells. DUOX2 activity was enhanced by a modest increase in intracellular Ca2+ concentration, similar to that induced by Ca2+ microdomains that arise in resting T cells through different T cell receptor (TCR)-independent mechanisms. In addition, DUOX2 was activated in vitro by phosphorylation of threonine-789 mediated by PKA Cβ or PKCθ, and genetic deficiency of PKA Cβ2 or PKCθ decreased NAADP-dependent Ca2+ microdomain formation in T cells. PKA Cβ2 was activated downstream of adenosine A2A receptors, independently of the TCR. In contrast, PKCθ was activated by the tyrosine kinase LCK downstream of TCR stimulation. Inhibition of A2A receptors or PKCθ to prevent full DUOX2 activation decreased the production of the proinflammatory cytokine IL-17 by effector T cells. Thus, full stimulation of NAADP signaling that is critical for T cell activation requires integration of multiple TCR-independent and -dependent signals with different spatiotemporal characteristics by DUOX2, a fine-tuning mechanism that could be relevant for inflammation.